Standards for scientific and industrial equipment have specified ever finer and more accurate component positioning alignments within narrow ranges. Particularly, optical and laser equipment require small displacement capabilities.
Adjustable mirror mounts and X, Y, Z positioners have been used in optical bench elements which were designed to achieve selective and fine movements. In such X, Y, Z positioner designs, three finely pitched micrometric screws drove three sliding or rolling carriages. These carriages and their respective drive screws are structurally interconnected into a three dimensional displacement drive assembly. Spring loading of such interconnected elements is used to eliminate play in the carriage ways; however, undesirable cumulative error displacements seriously interfere with the operation of the positioner assembly in the micrometric range. As optics and fiber optics applications have increased, design demands have dictated optical work benches capable of extremely small displacements, down into the ranges of wavelengths of the light spectrum. The more minute the desired displacement, the greater tha naturally occurring effect of cumulative error resulting from carriage play and the spring loading of interconnected assembly elements.
Previous attempts at addressing the problems of cumulative error and mechanical backlash include adjustable mirror mount devices employing flexure pin hinges for adjusting two angles to achieve substantially reduced backlash. Flexure pins used as low backlash hinges for small angular displacements are featured in Laser and Fabry Perot cavity alignment structures. Flexure pivot principle based devices include the "Micro Positioning Base" manufactured by Newport Corporation (NRC); and, one dimensional flexure pivot stages assembled by Physitec (catalog numbers 42-1050 and 42-1055).
U.S. Pat. No. 4,139,948 issued to Tsuchiya discloses a micromanipulator based on the principle of the differential lever, wherein a fine displacement is achieved by the interaction of two separate micrometers 36 and 38 (FIG. 1) to produce an accuracy of 0.1 to 0.2 micron Linear Movement. Such a device was used to align the core ends of optical fibers.
U.S. Pat. No. 4,331,384 to Eisler is directed to an optomechanical system, built up of basic elements with a number of orthogonal degrees of freedom. This system claims to achieve three degrees of freedom down to a resolution in each of three directions of 0.2 micrometers; the overall displacement in the interferometrical range equal a movement which is achieved by a separate assembly in each direction of movement. A lever mechanism with a high transmission ratio through a differential and standard micrometer screw is used to achieve this fine resolution, and is discussed in U.S. Pat. No. 4,209,233, also to Eisler.
As industry standards and optics requirements have evolved, interferometrical resolution and accuracy is affected both by the inherent backlash in each orthogonal degree of freedom as well as cross-talk between the independent elements, where each element controls movement in a separate direction and degree. While problems like backlash and cross-talk have not been overwhelming in the micrometric ranges of displacement, these problems are of greater moment in the nanometric ranges which include optical resolutions of the order of magnitude of the wave length of light. Therefore, there is a need for a more precise and sensitive optical positioner or bench tool which is capable of accurate operation in more precise measurements and ranges.